Answer
blue
Work Step by Step
First we consider equation 35-14:
$d \sin \theta = m \lambda $ where $m=0,1,2,3,....$ (maxima)
We can see that as the wavelength increases, the angle will also increase; therefore light with a lower wavelength will be closer to the center. If we compare red and blue light; blue light has a shorter wavelength and therefore will be closer to the center than the red light.
